Effects of Carbohydrate Restriction on Body Weight and Glycemic Control in Individuals with Type 2 Diabetes: A Randomized Controlled Trial of Efficacy in Real-Life Settings

Replacing dietary carbohydrate with protein and fat improves lipoprotein subclass profile and liver fat in type 2 diabetes independent of body weight: evidence from 2 randomized controlled trials

BACKGROUND

Dyslipidemia with elevated concentrations of triacylglycerol-rich lipoproteins (TRLs), small-dense LDL, and reduced HDL is linked to hepatic steatosis and promotes atherogenesis in type 2 diabetes (T2D).

OBJECTIVES

We aimed to analyze whether moderate carbohydrate restriction reduces liver fat in T2D independent of changes in body weight and whether this is accompanied by parallel improvements in plasma lipoprotein subclasses.

METHODS

We determined the density profile of circulating lipoproteins in patients with T2D from 2 previous randomized controlled trials. In the isoenergetic study, 30 participants were allocated in a crossover design to 6 + 6 wk of an isocaloric carbohydrate-reduced high-protein (CRHP, C/P/F = 30/30/40 E%) or conventional diabetes (CD, C/P/F = 50/17/33 E%) diet aimed at weight maintenance. In the hypoenergetic study, 72 participants were allocated in a parallel-group design to 6 wk of a hypocaloric CRHP or CD diet aimed at matched ∼6% weight loss. Both studies provided all meals from a metabolic kitchen to maximize adherence.

RESULTS

In the isoenergetic study, the CRHP diet reduced TRL (mean: -33%; 95% CI: -48%, -14%) and LDL5 (mean: -16%; 95% CI: -26%, -4%) and increased HDL2/HDL3 (mean: 10%; 95% CI: 0%, 22%) compared with the CD diet. In the hypoenergetic study, weight loss induced by CRHP diet tended to reduce TRL (mean: -16%; 95% CI: -30%, 1%), reduced LDL5 (mean: -13%; 95% CI: -22%, -3%), and increased HDL2/HDL3 (mean: 11%; 95% CI: 1%, 22%) compared with an equivalent weight loss induced by CD diet. The CRHP diet decreased intrahepatic triacylglycerol (IHTG) more than the CD diet (isoenergetic: -55%; 95% CI: -74%, -22%; hypoenergetic: -26%; 95% CI: -45%, 0%), and changes in IHTG correlated directly with changes in TRL and LDL5 (r = 0.36-0.55; P < 0.01 for all) in both studies.

CONCLUSIONS

Replacing dietary carbohydrate with protein and fat improves dyslipidemia in T2D independently of changes in body weight, by inducing an atheroprotective shift in the lipoprotein particle profile possibly facilitated by reduced IHTG accumulation. These trials were registered at clinicaltrials.gov as NCT02764021 (https://clinicaltrials.gov/study/NCT02764021?term=NCT02764021&rank=1) and NCT03814694 (https://clinicaltrials.gov/study/NCT03814694?term=NCT03814694&rank=1).

A network meta-analysis of the comparative efficacy of different dietary approaches on glycaemic control and weight loss in patients with type 2 diabetes mellitus and overweight or obesity

Background: Despite considerable literature supporting the benefit of dietary interventions in individuals with type 2 diabetes mellitus (T2DM) and overweight/obesity, which diet works best is currently unknown. We conducted a systematic review and network meta-analysis (NMA) to evaluate the comparative effectiveness of different dietary approaches in overweight or obese adults with T2DM. Methods: We searched EMBASE, the Cochrane Central Register of Controlled Trials (CENTRAL) and PubMed up till July 2023 for controlled studies using different dietary approaches. Next, we updated the literature search to September 2024 but found no new relevant studies. Glycated hemoglobin A1c (HbA1c) levels and body weight were used as primary outcomes. For each outcome, a pooled effect was determined for each intervention compared with other interventions. Mean differences (MDs) and 95% confidence intervals (95% CIs) were computed. The surface under the cumulative ranking curve (SUCRA) was used for ranking the dietary approaches. Moreover, confidence was assessed using the CINeMA (confidence in network meta-analysis) framework. Results: Overall, 31 trials that compared eight diet interventions (Mediterranean, moderate-carbohydrate, low-carbohydrate, vegetarian, low-glycaemic index/load, low-fat, high-protein and control diets) and involved 3096 people were included. In terms of glycemic control, the Mediterranean diet yielded the best ranking (SUCRA: 88.15%), followed by the moderate-carbohydrate diet (SUCRA: 83.3%) and low-carbohydrate (LC) diet (SUCRA: 55.7%). In terms of anthropometric measurements, the LC diet (SUCRA: 74.6%) ranked first, followed by the moderate-carbohydrate diet (SUCRA: 68.7%) and vegetarian diet (SUCRA: 57%). These results also showed that the differences in almost all dietary patterns regarding anthropometric measurements were mostly small and often trivial. Conclusions: In summary, the Mediterranean diet was the most efficient dietary intervention for the improvement of glycaemic control, and the LC diet obtained the highest score for anthropometric measurements in individuals with T2DM and concurrent overweight/obesity.

Association of low-carbohydrate diet scores and type 2 diabetes in Chinese rural adults: The Henan Rural Cohort Study

PURPOSE

To investigate the association between low-carbohydrate diet scores (LCDs) and the risk of type 2 diabetes in rural China.

METHODS

A total of 38,100 adults were included in the Henan Rural Cohort Study. Macronutrient intake was assessed via a validated food-frequency questionnaire to create low-carbohydrate diet (LCD) scores. Multivariate logistic regression models and subgroup analysis were performed to estimate the odds ratio (OR) and 95% confidence interval (95% CI).

RESULTS

After multivariable adjustment, participants with a high total low-carbohydrate diet score have a high risk of T2D (extreme-quartile OR = 1.23, 95% CI: 1.04-1.41; P = 0.007), whereas plant-based LCD score is not related to T2D risk. Among individuals with a BMI < 24 (extreme-quartile OR = 1.22, 95% CI: 1.01-1.47; P < 0.001) or high levels of physical activity (extreme-quartile OR = 1.42, 95% CI: 1.17-1.72; P < 0.001), the animal-based LCD score is positively correlated with the risk of T2D.

CONCLUSION

Among Chinese rural populations, high-fat-low carbohydrate diet is associated with an increased risk of type 2 diabetes. High intake of animal protein and fat also increases T2D risk in those who are overweight or have high physical activity.